REFLECTOR: Unbalanced fuel flow in flight

Darrell & Nora Kufalk kufalk at wi.rr.com
Sun Mar 13 18:45:26 CDT 2011


Glen,

 

I would agree with you.  In my roundabout way, I meant to say, after all fuel lines, vent lines and fuel caps are all confirmed working correctly, and you still have uneven flow, the most likely cause is rigging.

 

Darrell

 

 

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Glenn Babcock
Sent: Sunday, March 13, 2011 4:48 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Unbalanced fuel flow in flight

 

While I agree that proper rigging is important and can cause the tanks to be unbalanced, respectfully I disagree that a properly rigged Velocity will always have balanced fuel flow. If the fuel cap leaks then the Venturi effect will pull a lot of air from the tank, causing a drop in pressure inside that tank that will cause it to be higher than the other side. My Velocity is properly rigged and I had this happen. A little fuel lube on the O-rings fixed it. 

Regards,

 

Glenn

 


On Mar 13, 2011, at 1:09 PM, "Darrell & Nora Kufalk" <kufalk at wi.rr.com> wrote:

Richard,

 

In my opinion, you can categorize Velocitys into 2 groups.  Those that fly crooked and have unbalanced fuel flows and those that have been corrected to fly straight and have even fuel flow.  The Velocity that is built and flies perfectly straight out of the box is such a rarity as to be considered nonexistent (by a first time builder anyway).  I spent an insane amount of time leveling and measuring the wings and still ended up with an out of rig airplane.  Luckily this is a very fixable problem.  You are on the right track to fixing this.  Check all the things you have checked and all the things mentioned with the fuel lines, vent lines and fuel caps.  When you are certain they are eliminated, go after the rigging.  

Get that rigging board out and check the main wings again.  Use a precision level not a hardware store cheapie.  Get the airplane perfectly level.  Then measure the difference between the rigging of the left main wing to the right main wing.  Absolute angle is less important here than the difference between the two.  You will most likely need to shim one side or the other.  Regular washers won’t help here.  You need to add shims of 0.010” to 0.020” in thickness at a time.  Stainless steel shim stock works good for this.  I was able to get my wings within 1/10 of a degree of each other by doing this after 2 or 3 tries.  I went out and flew and still had uneven fuel flow.  Next I went after the rudders.  I began by pressing the left rudder pedal and holding it for as long as I could stand.  The airplane flew straighter and the fuel flows began to balance out.  I then glued pieces of mixing sticks under the left rudder to hold it out without pressing the rudder pedal.  I found 2 mixing sticks made the plane fly perfectly straight and my fuel tanks began flowing very evenly.

Those 2 mixing sticks are still in place but you would never know it by looking.  They are buried in some micro and the lower winglet was adjusted to match the rudder.  Scott Swing explained how to do this to make it look good.  After painting you would never know this fix was made.

I’m really happy I spent the time to fix this.  Knowing your plane flies straight and level is worth the hassle.

 

Darrell

 

 

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Andrew Judge
Sent: Sunday, March 13, 2011 10:16 AM
To: 'reflector at tvbf.org'
Subject: Re: REFLECTOR: Unbalanced fuel flow in flight

 

Mine has drained uneven for at least 1/2 the hours I've put on it (300+). You can check the caps by moving them and if the flow follows the cap, then it's probably a cap issue. Not sure how anyone has an airtight seal with caps? Doesn't seem possible. 

Sometimes mine drains down to 5 gallons before taking on the other side. I've learned that it will always drain out, but it is annoying. Even more annoying it a flickering sump low indication - which I get at times but not affiliated with the fuel flow. 

Andy

 


  _____  


From: reflector-bounces at tvbf.org <reflector-bounces at tvbf.org> 
To: Reflector <reflector at tvbf.org> 
Sent: Sun Mar 13 11:02:25 2011
Subject: Re: REFLECTOR: Unbalanced fuel flow in flight 

Richard,
This is just a "me too," to what has already been said.  I have an XL with the Atkinson clear fuel sight gauges in the cabin.  I used to check only the RH one in flight and see that it was about right, and never compared it closely to the other which is difficult to see for me due to have to crane my neck around or even half climb out of the pilot seat.  I have a forward facing fuel vent tube out the belly, with a small whole drilled on the back face for an alternate orifice in the chance of ice.  Well I got into a brief but heavy transit thru about 1000 to 1500 feet of cloud in central Penn that surprised me, and it was slow to come off since once on top the outside air was too cold.  So I began to fret that my vent tube was liked iced some.  So I looked at both my sight gauges and they were an inch (aprox 5 gal) or more apart and it scared the hell out of me.  Since then I have learned that they do sort of rachet back and forth and do not come down exactly even.  The flight was uneventful.  
 
John Abraham's yaw string idea is ancient, and quick and easy to do.  Leave it on there for a whole series of flights.   A small hunk of masking tape and a foot or so of knitting yarn works great.  If you have some one with you, you can try scribing your yaw angle if it is off any w/ a water magic marker so you have a ref point for any changes or experiments you might try.  Good luck, but also be sure your vent system works right or it could completely stop your fuel feed.  It's dirt simple, but vital...I'm sure you know that.  
 
Terry
 
From: richard at naples-air-center.com
Date: Sun, 13 Mar 2011 08:27:03 -0400
To: reflector at tvbf.org
Subject: REFLECTOR: Unbalanced fuel flow in flight

Friday I completed my second test flight.  I found that all the fuel drained from the right side and none from the left while on the one hour flight. (I actually cut the flight short due to this.)
 
When I landed I verified with my fuel stick that all the fuel did co e from the right tank. 
 
For troubleshooting: 
 
1) I removed the line from the left tank to the sump tank and verified that fuel did flow freely from the left tank. 
 
2) Removed the vent line from the left tank and tested the line in the direction of the left tank and in the direction to the vent/overflow block at the top of my firewall using compressed air. 
 
3) I checked the check valve for the air for correct operation in both directions and verified it was installed in the correct direction for air to enter and that fuel would not vent into the cabin. 
 
4) Verified the overflow line was clear by using compressed air. 
 
I know the picture is hard to follow but this is the fuel system:
 


Richard Sent from my iPhone 4
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